.Net Core Identity: User update not working

Hi,

After a user is registered and logged in, if I try to update their profile I can only update the phone number. I have 2 custom fields first name and last name but when I try to edit them it will revert back to the old value.

public async Task<IActionResult> OnPostAsync()
{
    var user = await _userManager.GetUserAsync(User);
    if (user == null)
    {
        return NotFound($"Unable to load user with ID '{_userManager.GetUserId(User)}'.");
    }

    if (!ModelState.IsValid)
    {
        await LoadAsync(user);
        return Page();
    }

    var phoneNumber = await _userManager.GetPhoneNumberAsync(user);
    if (Input.PhoneNumber != phoneNumber)
    {
        var setPhoneResult = await _userManager.SetPhoneNumberAsync(user, Input.PhoneNumber);
        if (!setPhoneResult.Succeeded)
        {
            StatusMessage = "Unexpected error when trying to set phone number.";
            return RedirectToPage();
        }
    }

    if (Input.FirstName != user.FirstName)
    {
        user.FirstName = Input.FirstName;
    }
    if (Input.LastName != user.LastName)
    {
        user.LastName = Input.LastName;
    }

    await _signInManager.RefreshSignInAsync(user);
    StatusMessage = "Your profile has been updated";
    return RedirectToPage();
}